From b4cba4ed625ce7c88675616b3bbb237c28a926d1 Mon Sep 17 00:00:00 2001
From: Jon Prindiville <jprindiville@gadventures.com>
Date: Wed, 26 Apr 2017 11:43:56 -0400
Subject: [PATCH] Fixed #28144 -- Added FileSystemStorage.OS_OPEN_FLAGS to
 allow customization.

---
 django/core/files/storage.py |  9 ++++-----
 tests/file_storage/tests.py  | 39 ++++++++++++++++++++++++++++++++++++
 2 files changed, 43 insertions(+), 5 deletions(-)

diff --git a/django/core/files/storage.py b/django/core/files/storage.py
index 30788d6d75..b0168186ef 100644
--- a/django/core/files/storage.py
+++ b/django/core/files/storage.py
@@ -168,6 +168,9 @@ class FileSystemStorage(Storage):
     """
     Standard filesystem storage
     """
+    # The combination of O_CREAT and O_EXCL makes os.open() raise OSError if
+    # the file already exists before it's opened.
+    OS_OPEN_FLAGS = os.O_WRONLY | os.O_CREAT | os.O_EXCL | getattr(os, 'O_BINARY', 0)
 
     def __init__(self, location=None, base_url=None, file_permissions_mode=None,
                  directory_permissions_mode=None):
@@ -256,12 +259,8 @@ class FileSystemStorage(Storage):
 
                 # This is a normal uploadedfile that we can stream.
                 else:
-                    # This fun binary flag incantation makes os.open throw an
-                    # OSError if the file already exists before we open it.
-                    flags = (os.O_WRONLY | os.O_CREAT | os.O_EXCL |
-                             getattr(os, 'O_BINARY', 0))
                     # The current umask value is masked out by os.open!
-                    fd = os.open(full_path, flags, 0o666)
+                    fd = os.open(full_path, self.OS_OPEN_FLAGS, 0o666)
                     _file = None
                     try:
                         locks.lock(fd, locks.LOCK_EX)
diff --git a/tests/file_storage/tests.py b/tests/file_storage/tests.py
index 33dc699ab4..3a21ca9046 100644
--- a/tests/file_storage/tests.py
+++ b/tests/file_storage/tests.py
@@ -566,6 +566,45 @@ class CustomStorageTests(FileStorageTests):
         self.storage.delete(second)
 
 
+class OverwritingStorage(FileSystemStorage):
+    """
+    Overwrite existing files instead of appending a suffix to generate an
+    unused name.
+    """
+    # Mask out O_EXCL so os.open() doesn't raise OSError if the file exists.
+    OS_OPEN_FLAGS = FileSystemStorage.OS_OPEN_FLAGS & ~os.O_EXCL
+
+    def get_available_name(self, name, max_length=None):
+        """Override the effort to find an used name."""
+        return name
+
+
+class OverwritingStorageTests(FileStorageTests):
+    storage_class = OverwritingStorage
+
+    def test_save_overwrite_behavior(self):
+        """Saving to same file name twice overwrites the first file."""
+        name = 'test.file'
+        self.assertFalse(self.storage.exists(name))
+        content_1 = b'content one'
+        content_2 = b'second content'
+        f_1 = ContentFile(content_1)
+        f_2 = ContentFile(content_2)
+        stored_name_1 = self.storage.save(name, f_1)
+        try:
+            self.assertEqual(stored_name_1, name)
+            self.assertTrue(self.storage.exists(name))
+            self.assertTrue(os.path.exists(os.path.join(self.temp_dir, name)))
+            self.assertEqual(self.storage.open(name).read(), content_1)
+            stored_name_2 = self.storage.save(name, f_2)
+            self.assertEqual(stored_name_2, name)
+            self.assertTrue(self.storage.exists(name))
+            self.assertTrue(os.path.exists(os.path.join(self.temp_dir, name)))
+            self.assertEqual(self.storage.open(name).read(), content_2)
+        finally:
+            self.storage.delete(name)
+
+
 class DiscardingFalseContentStorage(FileSystemStorage):
     def _save(self, name, content):
         if content: